Ultrasonic and Viscoelastic Studies of Chain Entanglement in Polymer Solutions

Abstract

Whether a polymer chain forms a permanent or temporary entanglement or crosslink; one of the most drammatic effects which is observed is the modification of the dynamic spectrum exhibited by the polymer chain. The other manifestation of network formation is the observation of a modulus value which is directly related to the number of network points per unit volume. In general, we can divide networks into two types; firstly, those in which the chains between the network points are topographically defined in space — “rigid networks” and secondly, those that have flexible regions between junction points —“flexible networks”. The most characteristic feature of the dynamics of a polymer chain is its glass transition temperature - Tg. Above Tg, elements of the polymer chain can undergo co-operative molecular motion, below Tg only the uncorrelated motion of short elements of the backbone and side chains are possible. The division of the networks into rigid and flexible can be made on the basis of the glass transition temperature of the backbone polymer structure.